A numerical study of particle-laden flow around an obstacle: flow evolution and Stokes number effects

2021 ◽  
Author(s):  
Shengxiang Lin ◽  
Jianhua Liu ◽  
Huanxiong Xia ◽  
Zhenyu Zhang ◽  
Xiaohui Ao
Keyword(s):  
Numerical Study ◽  
Stokes Number ◽  
Flow Evolution ◽  
Particle Laden Flow

scholarly journals A Numerical Study of the Effect of Particle Size on Particle Deposition on Turbine Vanes and Blades

2021 ◽  
Vol 13 (5) ◽  
pp. 168781402110178
Author(s):  
Zhengang Liu ◽  
Weinan Diao ◽  
Zhenxia Liu ◽  
Fei Zhang
Keyword(s):  
Particle Size ◽  
Particle Deposition ◽  
Numerical Study ◽  
Stokes Number ◽  
Capture Efficiency ◽  
Particle Capture ◽  
Factors Affecting ◽  
Pressure Surface ◽  
Deposition Area ◽  
Turbine Vanes

Particle deposition could decrease the aerodynamic performance and cooling efficiency of turbine vanes and blades. The particle motion in the flow and its temperature are two important factors affecting its deposition. The size of the particle influences both its motion and temperature. In this study, the motion of particles with the sizes from 1 to 20 μm in the first stage of a turbine are firstly numerically simulated with the steady method, then the particle deposition on the vanes and blades are numerically simulated with the unsteady method based on the critical viscosity model. It is discovered that the particle deposition on vanes mainly formed near the leading and trailing edge on the pressure surface, and the deposition area expands slowly to the whole pressure surface with the particle size increasing. For the particle deposition on blades, the deposition area moves from the entire pressure surface toward the tip with the particle size increasing due to the effect of rotation. For vanes, the particle capture efficiency increases with the particle size increasing since Stokes number and temperature of the particle both increase with its size. For blades, the particle capture efficiency increases firstly and then decreases with the particle size increasing.

PREDICTION OF UNSTEADY STATES IN LID-DRIVEN CAVITIES FILLED WITH AN INCOMPRESSIBLE VISCOUS FLUID

2012 ◽  
Vol 23 (04) ◽  
pp. 1250030 ◽  
Author(s):  
FAYÇAL HAMMAMI ◽  
NADER BEN-CHEIKH ◽  
ANTONIO CAMPO ◽  
BRAHIM BEN-BEYA ◽  
TAIEB LILI
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Three Dimensional ◽  
Staggered Grid ◽  
Three Dimensional Flow ◽  
Driven Cavity ◽  
Flow Evolution ◽  
2D And 3D ◽  
Benchmark Solutions ◽  
Good Agreement

In this work, a numerical study devoted to the two-dimensional and three-dimensional flow of a viscous, incompressible fluid inside a lid-driven cavity is undertaking. All transport equations are solved using the finite volume formulation on a staggered grid system and multi-grid acceleration. Quantitative aspects of two and three-dimensional flows in a lid-driven cavity for Reynolds number Re = 1000 show good agreement with benchmark results. An analysis of the flow evolution demonstrates that, with increments in Re beyond a certain critical value Rec, the steady flow becomes unstable and bifurcates into unsteady flow. It is observed that the transition from steadiness to unsteadiness follows the classical Hopf bifurcation. The time-dependent velocity distribution is studied in detail and the critical Reynolds number is localized for both 2D and 3D cases. Benchmark solutions for 2D and 3D lid-driven cavity flows are performed for Re = 1500 and 6000.

LDA Measurements and Numerical Prediction of Pulsatile Laminar Flow in a Plane 90-Degree Bifurcation

1988 ◽  
Vol 110 (2) ◽  
pp. 129-136 ◽  
Author(s):  
J. M. Khodadadi ◽  
N. S. Vlachos ◽  
D. Liepsch ◽  
S. Moravec
Keyword(s):  
Laminar Flow ◽  
Numerical Study ◽  
Numerical Procedure ◽  
Stokes Number ◽  
Flow Rate Ratio ◽  
Velocity Measurements ◽  
Numerical Predictions ◽  
Dependent Variables ◽  
Separation Zones ◽  
Good Agreement

An experimental and numerical study of pulsatile laminar flow in a plane 90-degree bifurcation is presented. Detailed LDA velocity measurements of the oscillatory flow field have been carried out. The numerical predictions, which are based on an iterative, finite-difference numerical procedure using primitive dependent variables, are in good agreement with the measurements. The results show that one separation zone is established near the bottom wall of the main duct and another near the upstream wall of the branch. The location and size of the separation zones vary within the cycle and are influenced by the Reynolds number, the flow rate ratio, and the Stokes number.

Numerical study of the secondary phase dispersion in a particle-laden flow

2017 ◽  
Author(s):  
Matei-Razvan Georgescu ◽  
George-Madalin Chitaru ◽  
Costin Ioan Cosoiu ◽  
Ionut Brinza ◽  
Catalin Nae
Keyword(s):  
Numerical Study ◽  
Secondary Phase ◽  
Phase Dispersion ◽  
Particle Laden Flow

Validation of Particle-Laden Turbulent Flow Simulations Including Turbulence Modulation

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Yvonne Reinhardt ◽  
Leonhard Kleiser
Keyword(s):  
Numerical Study ◽  
Density Ratio ◽  
Particle Diameter ◽  
Stokes Number ◽  
Navier Stokes ◽  
Mean Flow ◽  
Turbulent Length Scale ◽  
Turbulence Modulation ◽  
Flow Simulations ◽  
Wide Range

The objective of the present numerical study is the validation of wall-bounded, turbulent particle-laden air flow simulations for a wide range of flow and particle parameters (i.e., flow and particle Reynolds numbers, Stokes number, particle-to-fluid density ratio, ratio of particle diameter to turbulent length scale) covering the one-, two- and four-way coupling regimes. The applied computational fluid dynamics (CFD) model follows the Eulerian two-fluid approach in a Reynolds-Averaged Navier–Stokes (RANS) context and is based on the kinetic theory of granular flow (KTGF) for closures concerning the particulate phase. The fluid turbulence is modeled applying a low-Reynolds-number k–epsilon turbulence model. The main focus is put on the modeling of turbulence coupling between the fluid and the particle phase. Different from common practice, the choice of a model accounting for turbulence modulation is made dependent on the prevailing coupling regime. For the case of four-way coupling, a new modulation model is suggested that well predicts turbulence augmentation and attenuation. The predictive capabilities of the present approach are evaluated by comparing simulation results to experimental benchmark data of various pipe and channel flows. Very good agreement with reference data is obtained for the mean flow and turbulence profiles of both phases.

An Experimental and Numerical Study of a Micro-Synthetic Jet in a Shallow Cavity

2008 ◽  
Author(s):  
Alexander Sinclair ◽  
Victoria Timchenko ◽  
John Reizes ◽  
Gary Rosengarten ◽  
Eddie Leonardi
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Maximum Velocity ◽  
Stokes Number ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Numerical Results ◽  
Transfer Rates ◽  
Micro Scale ◽  
Shallow Cavity

By disrupting laminar flow, micro-scale synthetic jets have the potential to significantly increase mixing and heat transfer rates in micro-devices. Due to the difficulty involved in performing measurements on the micro-scale, few experimental studies of micro-synthetic jets exist. In this paper we describe instantaneous velocity fields obtained by μPIV measurements in the vicinity of a synthetic jet orifice 24 μm in diameter issuing into a confined geometry. Numerical results for a synthetic jet operating under similar conditions have been used to help validate and clarify the experimental results. Comparisons between the experimental and numerical results during the expulsion phase of the actuator cycle for a synthetic jet with a Reynolds number (based on maximum velocity), Re = 239 and Stokes number, S = 9, indicate there is good agreement, thereby demonstrating that the μPIV technique can be used successfully for future studies. Experimental difficulties encountered are presented and methods of overcoming them discussed.

scholarly journals Particle behavior in a turbulent flow within an axially corrugated geometry

2021 ◽  
Vol 13 (8) ◽  
pp. 168781402110360
Author(s):  
Ghulam Mustafa Majal ◽  
Lisa Prahl Wittberg ◽  
Mihai Mihaescu
Keyword(s):  
Gas Flow ◽  
Numerical Study ◽  
Stokes Number ◽  
Particle Dispersion ◽  
Particle Behavior ◽  
Eddy Simulation ◽  
Recirculation Zones ◽  
Pipe Geometry ◽  
Turbulent Gas Flow ◽  
Inflow Conditions

In this numerical study particle behavior inside a sinusoidal pipe geometry is analyzed. The 3D geometry consists of three identical modules, with a periodic boundary condition applied to the flow in the stream wise direction. The incompressible, turbulent gas flow is modeled using a Large Eddy Simulation (LES) approach. Furthermore, the particle dynamics are simulated using a Lagrangian point force approach incorporating the Stokes drag and slip correction factor. Four different sizes of particles, corresponding to a Stokes number less than unity, are considered along with two different inflow conditions: continuous and pulsatile. The pulsatile inflow has an associated flow frequency of 80 Hz. The fluid flow through the sinusoidal pipe is characterized by weak flow separation in the expansion zones of the sinusoidal pipe geometry, where induced shear layers and weak recirculation zones are identified. Particle behavior under the two inflow conditions is quantified using particle dispersion, particle residence time, and average radial position of the particle. No discernible difference in the particle behavior is observed between the two inflow conditions. As the observed recirculation zones are weak, the particles are not retained within the cavities for a long duration of time, thereby reducing their likelihood of agglomerating.

Performance Degradation of Wind Turbine Airfoils due to Dust Contamination: A Comparative Numerical Study

2015 ◽  
Author(s):  
Aya Diab ◽  
Moataz Alaa ◽  
Ahmed Hossam El-Din ◽  
Hassan Salem ◽  
Zakaria Ghoneim
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Numerical Study ◽  
Leading Edge ◽  
Performance Degradation ◽  
Surface Contamination ◽  
Dust Particles ◽  
Turbine Airfoils ◽  
Particle Laden Flow ◽  
Contamination Sensitivity

Sand accumulation can pose significant problems to wind turbines operating in the dusty Saharan environments of the Middle East and North Africa. Despite its difficulty, sand particles can be to a great extent avoided using sealed power drive trains; however, surface contamination of the blades is certainly unavoidable. As a result, aerodynamic losses and even premature separation can be incurred. To mitigate such advert consequences and avoid significant power losses, the choice of properly designed airfoil sections with low contamination sensitivity is a must. Alternatively, mitigation techniques for premature separation may also be considered. In this paper the contamination sensitivity of a number of airfoil sections widely used in the wind turbine industry is compared. Additionally, the possibility of deploying a leading edge slat to mitigate the contamination-driven performance degradation of wind turbine airfoils is explored. A two dimensional CFD model of the particle laden flow over an airfoil section is developed by solving Navier-Stokes equations along with the SST k-ω turbulence model. Additionally, a particle deposition model has been deployed via FLUENT’s discrete phase modeling capability to simulate dust particles trajectories and hence predict their accumulation rate. The preliminary results obtained indicate that airfoil sections with low surface contamination sensitivity specifically designed for wind turbines perform better under dusty conditions. Furthermore installing a leading edge slat affects the aerodynamics of the particle laden flow and may therefore be used to mitigate the adverse effects of surface contamination that otherwise would require frequent cleaning which can be expensive.

scholarly journals Numerical Study of Particle Interaction in Gas-Particle and Liquid-Particle Flows: Part II Particle Response

2009 ◽  
Vol 1 (3) ◽  
pp. 245-262
Author(s):  
K. Mohanarangam ◽  
J. Y. Tu
Keyword(s):  
Numerical Model ◽  
Numerical Study ◽  
Particle Interaction ◽  
Stokes Number ◽  
Steady Increase ◽  
Liquid Particle ◽  
Mean Velocity ◽  
Subsequent Increase ◽  
The Mean ◽  
Inlet Conditions

In this paper the numerical model, which was presented in the first paper (Mohanarangam & Tu; 2009) of this series of study, is employed to study the different particle responses under the influence of two carrier phases namely the gas and the liquid. The numerical model takes into consideration the turbulent behaviour of both the carrier and the dispersed phases, with additional equations to take into account the combined fluid particle behaviour, thereby effecting a two-way coupling. The first paper in this series showed the distinct difference in particulate response both at the mean as well as at the turbulent level for two varied carrier phases. In this paper further investigation has been carried out over a broad range of particle Stokes number to further understand their behaviour in turbulent environments. In order to carry out this prognostic study, the backward facing step geometry of Fessler and Eaton (1999) has been adopted, while the inlet conditions for the carrier as well as the particle phases correspond to that of the experiments of Founti and Klipfel (1998). It is observed that at the mean velocity level the particulate velocities increased with a subsequent increase in the Stokes number for both the GP (Gas-Particle) as well as the LP (Liquid-Particle) flow. It was also observed that across the Stokes number there was a steady increase in the particulate turbulence for the GP flows with successive increase in Stokes number. However, for the LP flows, the magnitude of the increase in the particulate turbulence across the increasing of Stokes number is not as characteristic as the GP flow. Across the same sections for LP flows the majority of the trend shows a decrease after which they remain more or less a constant.

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